The present invention relates to spherical surface inspection equipment for optically examining the surface nature of a sphere to be examined such as a steel ball.
1. Description of the Prior Art
As illustrated in FIG. 1, spherical surface inspection equipment having the following structure is already known as the previously described type of spherical surface inspection equipment. Specifically, the spherical surface inspection equipment is comprised of a semi-circumferential array 53 which includes a plurality of pairs of flood-light element 51 and light-receiving element 52 arranged in a semi-circumferential pattern at uniform angular intervals. The semi-circumferential array 53 is positioned in a circumferential direction of a steel ball 54 which is a ball to be examined. The steel ball 54 is rotated around a support axis 55 in the direction designated by arrow Y. The surface nature of the steel ball 54 is determined on the basis of an electrical signal output from the light-receiving element 52 (this spherical surface inspection equipment will be hereinafter referred to as a "first conventional example").
As illustrated in FIG. 2, in the first conventional example, the light emitted from the flood-light element 51 is reflected from the surface of the steel ball 54, and the thus-reflected light is received by the light-receiving element 52 disposed at a given angle alpha in relation to the flood-light element 51. The light-receiving element 52 converts the thus-received light into an electrical signal by a photoelectric converting element (not shown) such as a photo-diode. The thus-converted signal is output, via an amplifier and a gain control circuit (not shown). The level of the signal output from the light-receiving element 52 is compared with a given reference value, and the surface nature of the steel ball 54 is determined on the basis of the result of such comparison. In short, an examination is carried out as to whether or not there are imperfections such as flaws on the surface of the steel ball 54.
As illustrated in FIG. 3, there is another example of known spherical surface inspection equipment. The flood-light 56 (emitted from lighting equipment) incidents on the surface of the steel ball 54 which is rotating in the direction designated by arrow Z, and the light reflected from the surface of the steel ball 54 is collected into a point by use of a convex lens 57. An image of the thus-collected light is formed on a photoelectric converting element 58 such as a CCD (Charge-coupled Device). This example will be hereinafter referred to as a "second conventional example," and please refer to; e.g., Japanese Patent Unexamined Publication Nos. Sho-56-58643 and Sho-56-58644.
In the second conventional example, the photoelectric converting element 58 converts luminous energy into an electrical signal, and the nature of the spherical surface is determined on the basis of the level of the electrical signal. Specifically, a decision as to the presence or absence of imperfections in the steel ball 54 is performed on the basis of the level of the signal output from the photoelectric converting element 58. The second conventional example enables even the photoelectric converting element 58 having a small light-receiving area to examine the nature of the overall surface of the steel ball 54 by obliquely rotating at a given angle in relation to the steel ball 54.
However, in the first conventional example, it is necessary to examine the surface nature of the steel ball 54 with substantially identical sensitivity with regard to the diametrical dimension of the steel ball 54 (hereinafter referred to as the "size of the steel ball"). It is necessary to adjust the sensitivity of the spherical surface inspection equipment with regard to the detection of imperfections in the steel ball 54 every time the size of the steel ball changes. The allowable size of imperfections in a steel ball changes according to the size of the steel ball. In the case of the steel ball 54 having a small size, the allowable size of imperfections such as flaws must be set to a small size. In contrast, in the case of the steel ball 54 having a large size, the allowable size of imperfections may be set to a large size according to the size of the steel ball.
To prevent a decrease in the yield of steel balls, the sensitivity of the spherical surface inspection equipment is conventionally carried out according to the size of the steel ball so as to set the allowable size of imperfections corresponding to the size of the steel ball. For this reason, in the first conventional example, it is necessary to adjust and check the balancing of variations in the sensitivity of the photoelectric converting element to convert luminous energy into an electrical signal for each size of the steel ball.
In order to improve the capacity of the spherical surface inspection equipment to detect and resolve imperfections in view of surface nature, it is necessary to bring the light-receiving elements 52 as close to the vicinity of the steel ball 54 as possible such that the field of view of each light-receiving element 52 becomes narrow. For this reason, in the first conventional example, it is necessary to prepare the plurality of semi-circumferential arrays 53 tallying with the size of the steel ball beforehand. More specifically, in order to examine the nature of the surface of the steel ball 54 with high accuracy while the semi-circumferential array 53 is brought as close to the surface of the steel ball 54 as possible, it is necessary to manufacture a plurality of types of semi-circular arrays 53 having.-different pitch diameters according to the size of the steel ball. The spherical surface inspection equipment must be set by selection of a desired semi-circular array 53 corresponding to the size of the steel ball. It requires a lot of expense in time and effort to prepare for measurement.
In contrast, in the second conventional example, an image pick-up optical system determines a face-to-face distance of a steel ball to be examined (i.e., a first spacing "a" between the steel ball 54 and the lens 57 and a second spacing "b" between the convex lens 57 and the photoelectric converting element 58) and the magnification of an image (b/a). It is relatively easy to control in such a way that a relative distance; namely, the first spacing "a" and the second spacing "b," becomes constantly equal with respect to the steel ball 54 having a different size. However, it is difficult to ensure an image having uniform brightness by evenly illuminating the surface of the steel ball 54. More specifically, even when illumination light incidents on the surface of the steel ball 54, there is a great difference between the center of the illumination light and its periphery with regard to the angle at which the incoming light is reflected from the surface of the steel ball 54. It becomes difficult for the reflected light originated from the periphery of the illumination light to enter the lens 57, which in turn makes it impossible to produce an image having uniform brightness. The following method is conceivable. Specifically, as designated by a two-dot chain line in FIG. 3, a diffusing glass 59 is provided in the optical path of the illumination light, and the surface of the steel ball 54 is illuminated from many directions. The light reflected from the surface is diffused in various directions, and the diffuse reflections are collected into an image on the photoelectric conversion element 58.
However, if the diffusing glass 59 is disposed in the optical path, the illumination light is diffused in a wide range over the surface of the steel ball, thereby deteriorating the light-focusing efficiency of the convex lens 57. It is practically difficult to examine a wide range of the surface of the steel ball.
It is possible to change the capacity of the spherical surface inspection equipment to detect and resolve imperfections in terms of surface nature by changing the magnification of the optical system by use of the convex lens 57 according to the size of the steel ball. To obliquely rotate a steel ball, it is necessary to use a control roller manufactured according to the size of the steel ball and the degree of skew as disclosed in Japanese Patent Examined Publication (kokoku) Sho-42-17608, or it is necessary to provide the spherical surface inspection equipment with a skew mechanism as disclosed in Japanese Patent Unexamined Publication No. Sho-56-58643. Consequently, it is necessary to replace the previously-described component of the equipment each time the size of the steel ball changes. As in the first conventional example, it requires expense in time and effort to set the spherical surface inspection equipment. Further, the component is abraded or damaged as a result of contact between the component and the steel ball 54, thereby resulting in faulty oblique rotation of the steel ball. For this reason, in order to sufficiently ensure the result of inspection of the overall surface area of the steel ball 54, it is necessary for a person to carefully control the component. Furthermore, in practice, it is very difficult to manufacture a control roller and a skew mechanism capable of obliquely rotating the steel ball 54 having a diameter as small as 1 mm or thereabouts in view of production engineering. In short, as has been described above, the second conventional example has various problems with regard to production, as well as to the replacement and maintenance of a rotation control mechanism.